Britain's new Foreign Secretary Boris Johnson said Russia risks becoming a "pariah" state because of its air strikes on Syrian civilian targets.

"They drop one bomb and then they wait for the aid workers to come out, civilian people pulling the injured from the rubble, and then five minutes later they drop another bomb," Johnson said in an interview with Britain's Sun newspaper on September 30.

"We have evidence. We have good ground to believe that the Russians themselves have been doing that," he said. "We are trying to document that fully because that is in my view unquestionably a war crime."

A watchdog report on September 30 blamed nearly 10,000 civilians deaths on Russian strikes in the past year.

Johnson said Britain and the United States are looking at a "range of options" to ramp up pressure on Moscow, but "the single most potent weapon we have is shame."

"The world's attitude towards Russia has been hardening and I think people now believe that Russia is in danger of becoming a pariah nation."

"In the end, if [President Vladimir] Putin's strategy is the greatness and glory of Russia, then he risks seeing that turned to ashes as people view his actions with contempt."